Gas pressure control apparatus

ABSTRACT

Gas pressure control apparatus comprises a pressure body having a lid at the top, and divided into an inlet chamber partially bounded by the lid and communicating through a port with an outlet chamber. The inlet chamber contains a valve stack including a slam-shut valve and a pair of pressure regulating valves. The valve stack is held together by bolts, and is mounted on the lid by the bolts sliding through holes in a disc forming part of the lid. Springs urge the valve stack against the port in an essentially planar manner to maintain a good seal between the valve stack and the port.

TECHNICAL FIELD

The present invention relates to control installations for gastransmission and distribution systems, and particularly to apparatus forreducing and controlling the pressure and/or flow of gas in a pipeline.

BACKGROUND ART

In a gas transmission and distribution system, gas (i.e. fuel gas) isnormally transmitted at high pressure, but has to be distributed to endusers through local networks at a pressure which is relatively low andis also controlled fairly accurately. A pressure reducing station istherefore required for coupling the high-pressure transmission line tothe local distribution network.

Conventionally, a pressure reducing station comprises two streams inparallel, each stream containing an initial isolating valve, slam-shutvalve, a suitable number of pressure regulating (reducing) valvesdepending on the amount of pressure reduction required, and a finalisolating valve. A typical example of such a station is shown in our GB2 217 877 A. Such a station is normally located above ground, and thefact that the various valves in each stream are arranged in a linearsequence means that it normally occupies a good deal of space.

There has recently been increasing interest in the possibility ofpressure reducing stations which are largely buried. A buried stationhas various advantages: it is relatively unobtrusive, the liability ofaccidental or deliberate damage to it is reduced, and the noise emissionfrom it is reduced.

A buried station naturally requires a hole or pit to be dug, and it isdesirable to minimize the size of this pit. A somewhat different designhas therefore been developed for buried pressure reducing stations. Thebasic feature of a buried pressure reducing station, in its currentform, is a pair of pressure chambers, an inlet chamber and an outletchamber. The inlet chamber usually includes a filter, end communicateswith the outlet chamber through a valve stack (a valve assembly orcartridge) including a slam-shut valve and a suitable number of pressureregulating valves.

Various specific designs for such stations are known. The two chambersmay be physically separate units located adjacent to each other, or theymay be separate units but located in a common outer enclosure. Moreusually, however, they are separate regions of a single pressure bodydivided by internal walls. It is also common for such stations to belargely buried, as discussed above.

The valve stack has controls which have to be accessible from outsidethe chamber. In addition, the valve stack requires servicing at suitableintervals. The design of the station should therefore be such as to makethe valve stack easily accessible. This is commonly achieved by locatingthe chamber containing the valve stack towards the top of the pressurevessel and providing it with a lid which can be removed to provideaccess to the valve stack. This chamber therefore typically has a portor opening in its base with which the valve stack fits. The chambercontaining the valve stack may be either the inlet or the outletchamber.

The valve stack obviously has to have a good seal to the port betweenthe two chambers, to prevent the escape of high-pressure gas throughthat port directly to the outlet.

It would be possible to bolt the valve stack directly to the chamberwall surrounding the port. However, this would require access to thebottom of the chamber to release the valve stack, and this wouldgenerally be difficult. Some other sealing technique is thereforerequired.

A technique for achieving such a seal is to form the port and the matingend of the valve stack as accurately formed cylindrical surfaces, withone of them including a suitable seal (such as an O ring). The valvestack is attached to the lid of the chamber, and after servicing, thecombined lid and valve stack is lowered into the chamber, with thebottom end of the valve stack being inserted into the port. The lid canthen be locked in position, so locating the valve stack in position. Anexample of this technique, which can be described as a piston-type seal,is the system described in GB 2 024 650 A.

This technique has various drawbacks. The seal between the valve stackand the port is expensive and difficult to maintain, and it is difficultto monitor the insertion of the valve stack into the port and avoiddamage to the sealing parts of the valve stack and/or the port. Further,such a piston-type seal requires a substantial clearance between the twoparts being sealed together, to accommodate the O sealing ring; hence ifany damage (eg mechanical or chemical) occurs to the sealing ringcausing it to disintegrate, a leakage path of substantial size willresult.

The general object of the present invention is to provide an improvedtechnique for sealing a valve stack to a port, particularly a port in apressure reducing station.

SUMMARY OF THE INVENTION

The crux of the present invention lies in mating the valve stack withthe port in an essentially planar manner end spring loading the valvestack from the lid. A good seal is thereby maintained between the valvestack and the port.

Accordingly the present invention provides gas pressure controlapparatus comprising a pressure body having a removable lid and adivider substantially parallel with the lid dividing the body into afirst chamber bounded by the lid and a second chamber communicating withthe first chamber through a port forming part of the divider, the firstchamber containing a valve stack including a slam-shut valve and atleast one pressure regulating valve, the valve stack mating with theport in the divider, characterized in that the valve stack is mounted onthe lid and is spring urged into planar (abutting) sealing engagementwith the divider. The sealing engagement may be direct from the valvestack to the divider, or it may be indirect from the valve stack to anintermediate plate parallel to the divider and from the plate to thedivider, with planar (abutting) seals between the valve stack and theintermediate plate and between the intermediate plate and the divider.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a gas pressure controlapparatus in a gas transmission and distribution system according to thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The station comprises a pressure vessel 10 closed by a lid 11; thispressure vessel may be mostly buried below ground level 12. Internally,it contains an inlet chamber 13 and an outlet chamber 14, divided fromeach other by an internal wall 15. There is a single inlet 16 to theinlet chamber, while the outlet chamber has a main outlet 17 and asubsidiary outlet 18, which may be used eg for providing access tooutlet chamber 14 to sense the pressure therein. The pressure body 10 isin the form of a cylinder with a rounded end and the second chamber 14is in the form of a cylinder with a rounded end contained wholly withinthe pressure body 10.

The outlet chamber 14 is closed at the top by a divider 20 which has aport 21 in it. A valve stack 22 is held in sealing contact with the port21, and provides a communicating path from the inlet chamber 13 to theoutlet chamber 14. More precisely, the inlet chamber 13 has an innerspace 30 separated from its main volume by a filter 31, which filtersout any particulate impurities in the gas. The slam-shut valve 23 has aclosure member 32 and a seating 33; the valve is normally open, allowinggas to pass from the inner space 30 of the inlet chamber into the top ofthe valve stack 22.

The valve stack consists of a slam-shut valve 23 and two regulatingvalves 24 and 25 connected in series. The slam-shut valve is normallyopen, and is controlled by control means 34 located above the lid 11 toclose and so cut off all flow of gas through the station eg in the eventof some serious fault in the distribution system. The regulating valves24 and 25 are controlled by flexible control lines 35 and 36 to controlthe flow of gas through the station, these control lines being fed byfurther control means (not shown) located outside the pressure vessel,e.g. attached to the top of the lid 11. In general, the control meanssense the pressure in the distribution system fed from the outlet 17 andadjust the regulating valve to maintain this pressure constant.

More specifically, the pressure of the distribution system downstreamfrom outlet 17 is sensed via subsidiary outlet 18 by means of aconventional pressure sensor, not shown, and communicated to the controlmeans. The control means adjusts the regulating valve 25 to maintainthis pressure steady. Regulator valve 25 is the primary working valve,used to control the flow through the system and thus the outletpressure. Valve 24 is a monitor or back-up valve which is normally fullyopen and is used only if the primary regulator valve fails to controlthe outlet pressure adequate. Thus, should a fault develop withregulating valve 25 which results in the distribution system pressure inchamber 14 and outlet 17 increasing, the control means will sense thisincrease and bring regulating valve 24 into control as a safetyoverride. The slam-shut valve 23 is a second safety device and will beused only if both regulator valves 24, 25 fail, i.e., fail to stop theflow when required.

The regulating valves form part of a normal pressure control system.This control system operates in a continuous manner responsive tocontinuous changes in both inlet and outlet conditions, with the valvesthemselves operating sequentially. If the inlet pressure rises, thevalves close slightly to stop the outlet pressure from rising; if theload demand on the outlet rises, the outlet pressure will tend to fall,and the valves open slightly to keep the pressure up. The outletpressure is sensed via subsidiary outlet 18. It is not necessary tosense the inlet pressure, as standard control techniques can be used toadjust the valve positions according to the outlet pressure until theoutlet pressure is brought to the desired valve.

The regulating valves may be of any convenient type, e.g. diaphragmvalves or axial flow valves (wafer valves).

A diffuser 37 is mounted in and projects through the port 21 into theoutlet chamber 14, and diffuses the gas entering that chamber via thevalve stack and the port.

The valve stack is held together by a set of bolts 40 (only one of whichis shown). The two regulating valves 24 and 25 are held between a pairof discs 41 and 42, with the bolts 40 engaging with threaded holes indisc 41 and nuts 43 being tightened to hold the regulating valves 24 and25 and the discs 41 and 42 as a rigid assembly. There are conventionalgaskets (not shown) between the various valves of the valve stack.

The seating 33 of the slam-shut valve 23 is attached to the disc 42. Theclosure member 32 of the slam-shut valve has a shaft 44 which extendsthrough the lid 11 to the slam-shut control means 34. A spring 45 is incompression between the lower end of the slam-shut control means 34 andthe closure member 32 of the slam-shut valve. This slam-shut valve isurged closed by this spring, and is normally held open against thespring force by the control means 34 holding the shaft 44 upwards.

The valve stack is held on the underside of the lid 11 by means of aplate 46, which has an upwards extension 52 welded to the lid 11. Thebolts 40 can slide freely through the plate 46; the valve stack is urgeddownwards by springs 47 on the bolts, and its downward travel is limitedby nuts 48 at the top of the bolts.

When the station is being assembled, the lid 11 is initially off thepressure vessel 10, and the valve stack 22 is at the lower limit of itstravel away from the lid. The lid and valve stack assembly is loweredinto position in the pressure vessel, so that the bottom disc 41 of thevalve stack rests on the top 20 of the outlet chamber 14, with a sealbetween them.

In point of fact, the disc 41 does not rest directly on the chamber top20. There is a further plate 49 between them, carrying the filter 31,and there is a seal 50 between disc 41 and plate 49 and a seal 51between plate 49 and chamber top 20. However, this does not affect theprinciples involved.

The plate 49 may be bolted to the top 20 of the inner chamber 14 ifdesired. The upper end of the diffuser 37 can conveniently projectupwards above the level of the top of this plate and engage with thelower end of the valve stack 22, to assist in locating the valve stack.

Once the lid and valve stack assembly has been positioned, the lid isthen lowered further to engage with the rim of the vessel 10 and lockedthereto in a conventional manner. This forces the plate 46 to movedownwards on the bolts 40, compressing the springs 47 and so compressingthe seals 50 and 51. The inlet and outlet chambers are thus sealed fromeach other, with the only communication between them being via the valvestack 22.

The sliding of plate 46 down the bolts involves relative movementbetween the control means 34 of the slam-shut valve 23 and the seating33 of this valve. However, the operation of this valve is not effectedby this, because this valve is an on-off valve. In one position, thechamber member 32 is in the up position, far enough from the seating 33for the flow of gas through it to be uneffected by the precise positionof the closure member relative to the seating; and in the otherposition, the closure member is lowered into engagement with theseating, and this is also uneffected by the precise distance throughwhich it has to travel for this.

It will be appreciated, upon review of the description herein, that theflow path of gas through the pressure vessel 10 is as follows. Gasenters the inlet chamber 13 via inlet 16. The gas encounters filter 31,which filters out any particular impurities in the gas. After emanatingfrom filter 31, gas enters the normally open slam-shut valve 23, flowsthrough regulating valves 24 and 25, through port 21 in divider 20 tooutlet chamber 14, then exits the pressure vessel 10 by means of mainoutlet 17.

We claim:
 1. Gas pressure control apparatus comprising a pressure body(10) having a removable lid (11) and a divider (2) substantiallyparallel with the lid dividing the body into a first chamber (13)bounded by the lid (11) and including an inlet port receiving gas and asecond chamber (14) communicating with the first chamber through a port(21) forming part of the divider (20) and including an outlet portthrough which gas exits from the pressure body (10), the first chamberincluding a seal comprising a valve stack (22) including a slam-shutvalve (23) and at least one pressure regulating valve (24, 25), thevalve stack (22) mating with the port (21) in the divider (20), whereinthe valve stack (22) is mounted on the lid (11) and is spring urged (at47) into planar (abutting) sealing engagement with the divider (20). 2.Gas pressure control apparatus according to claim 1 wherein the firstchamber (13) is an inlet chamber and the second chamber (14) is anoutlet chamber.
 3. Gas pressure control apparatus according to claim 1wherein a plurality of bolts (40) which hold together the valves (23,24, 25) of the valve stack (22) and which extend beyond the valve stack(22) towards the lid (11) and have springs (47) thereon which performthe spring urging.
 4. Gas pressure control apparatus according to claim3 wherein the bolts (40) are held captive on a disc (46) attached to thelid (11) and against which the springs (47) bear.
 5. Gas pressurecontrol apparatus according to claim 1 wherein the valve stack (22)includes a diffuser (37) projecting through the port (21).
 6. Gaspressure control apparatus according to claim 1 wherein a filter (31)surrounding the valve stack (22).
 7. Gas pressure control apparatusaccording to claim 6 wherein the filter (31) is closed by a plate (49)held in planar sealing engagement between the valve stack (22) and theport (21).
 8. Gas pressure control apparatus according to claim 1wherein the pressure body (10) is in the form of a cylinder with arounded end and the second chamber (14) is in the form of a cylinderwith a rounded end contained wholly within the pressure body (10).
 9. Aseal for un underground gas pressure control apparatus including apressure body (10) having a removable lid (11) and a divider (2)substantially parallel with the lid dividing the body into a firstchamber (13) bounded by the lid (11) and including an inlet portreceiving gas and a second chamber (14) communicating with the firstchamber through a port (21) forming part of the divider (20) andincluding an outlet port through which gas exits from the pressure body(10), the seal comprising a valve stack (22) disposed in the firstchamber and including a slam-shut valve (23) and at least one pressureregulating valve (24, 25), the valve stack (22) mating with the port(21) in the divider (20) and mounted on the lid (11) and is spring urged(at 47) into planar (abutting) sealing engagement with the divider (20).